Transmission and control method for transmission

ABSTRACT

A transmission includes a sub-transmission mechanism, a variator having lower shift responsiveness than the sub-transmission mechanism, and a controller configured to carry out a coordinated shift for changing a speed ratio of the variator in a direction opposite to a changing direction of a speed ratio of the sub-transmission mechanism as the sub-transmission mechanism is shifted so that a through speed ratio reaches a target through speed ratio. The controller sets a target speed ratio of the sub-transmission mechanism on the basis of the target through speed ratio and an actual speed ratio of the variator in carrying out the coordinated shift.

TECHNICAL FIELD

The present invention relates to a transmission and a control method fortransmission.

BACKGROUND ART

In a transmission, a stepped transmission mechanism is provided inseries with a continuously variable transmission mechanism and acoordinated shift may be carried out to change a speed ratio of thecontinuously variable transmission mechanism in a direction opposite toa changing direction of a speed ratio of the stepped transmissionmechanism as the stepped transmission mechanism is shifted. Such atechnique is disclosed, for example, in JP5-79554A.

SUMMARY OF INVENTION

Shift responsiveness of a transmission mechanism differs, for example,depending on a structure and the like. If a shift delay occurs in thetransmission mechanism having lower shift responsiveness during acoordinated shift, the coordinated shift is lost and an unintendedvehicle speed variation or the like is induced. Thus, a sense ofincongruity may be given to a driver.

The present invention was developed in view of such a technical problemand aims to provide a transmission and a control method for transmissioncapable of eliminating a sense of incongruity given to a driver as aresult of a lost coordinated shift even if a first transmissionmechanism and a second transmission mechanism differ in shiftresponsiveness.

A transmission according to a certain aspect of the present inventionincludes a first transmission mechanism provided in a power transmissionpath for transmitting power from a drive source of a vehicle to drivewheels, a second transmission mechanism provided in series with thefirst transmission mechanism in the power transmission path, the secondtransmission mechanism having lower shift responsiveness than the firsttransmission mechanism, and a shift control unit configured to carry outa coordinated shift for changing a speed ratio of the secondtransmission mechanism in a direction opposite to a changing directionof a speed ratio of the first transmission mechanism as the firsttransmission mechanism is shifted so that a through speed ratio, thethrough speed ratio being an overall speed ratio of the first and secondtransmission mechanisms, reaches a target through speed ratio. The shiftcontrol unit sets a target speed ratio of the first transmissionmechanism on the basis of the target through speed ratio and an actualspeed ratio of the second transmission mechanism in carrying out thecoordinated shift.

According to another aspect of the present invention, a control methodfor a transmission with a first transmission mechanism provided in apower transmission path for transmitting power from a drive source of avehicle to drive wheels, and a second transmission mechanism provided inseries with the first transmission mechanism in the power transmissionpath, the second transmission mechanism having lower shiftresponsiveness than the first transmission mechanism is provided. Thecontrol method for the transmission includes carrying out a coordinatedshift for changing a speed ratio of the second transmission mechanism ina direction opposite to a changing direction of a speed ratio of thefirst transmission mechanism as the first transmission mechanism isshifted so that a through speed ratio, the through speed ratio being anoverall speed ratio of the first and second transmission mechanisms,reaches a target through speed ratio, and setting a target speed ratioof the first transmission mechanism on the basis of the target throughspeed ratio and an actual speed ratio of the second transmissionmechanism in carrying out the coordinated shift.

According to these aspects, a target sub-speed ratio of the firsttransmission mechanism having higher shift responsiveness than thesecond transmission mechanism is set on the basis of the target throughspeed ratio and the actual speed ratio of the second transmissionmechanism in carrying out a coordinated shift. Thus, a deviation betweenthe target through speed ratio and an actual through speed ratio can beprevented. Thus, even if the first and second transmission mechanismsdiffer in shift responsiveness, a loss of the coordinated shift can besuppressed, with the result that a sense of incongruity given to adriver can be eliminated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an essential part of a vehicle including atransmission,

FIG. 2 is a graph showing an example of a shift map,

FIG. 3 is a flow chart showing an example of a control executed in anembodiment,

FIG. 4A is a first chart showing a target SEC rotation speed correction,

FIG. 4B is a second chart showing the target SEC rotation speedcorrection, and

FIG. 5 is a chart showing a variator shift speed correction.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment of the present invention is described withreference to the accompanying drawings.

FIG. 1 is a diagram showing an essential part of a vehicle including atransmission 100. The vehicle includes an engine 1, a torque converter2, a variator 20, a sub-transmission mechanism 30, a vehicle axle part 4and drive wheels 5.

The engine 1 constitutes a drive source of the vehicle. The torqueconverter 2 transmits power via fluid. The variator 20 and thesub-transmission mechanism 30 convert an input rotation speed and outputa rotation speed corresponding to a speed ratio. The vehicle axle part 4is configured to include a reduction gear, a differential device and adrive axle. Power of the engine 1 is transmitted to the drive wheels 5via the torque converter 2, the variator 20, the sub-transmissionmechanism 30 and the vehicle axle part 4.

The variator 20 is a continuously variable transmission mechanism andincludes a primary pulley 21, a secondary pulley 22 and a belt 23.Primary is referred to as PRI and secondary is referred to as SEC below.

The PRI pulley 21 includes a fixed pulley 21 a, a movable pulley 21 band a PRI chamber 21 c. In the PRI pulley 21, a PRI pressure is suppliedto the PRI chamber 21 c.

The SEC pulley 22 includes a fixed pulley 22 a, a movable pulley 22 band a SEC chamber 22 c. In the SEC pulley 22, a SEC pressure is suppliedto the SEC chamber 22 c.

The belt 23 is wound on a V-shaped sheave surface formed by the fixedpulley 21 a and the movable pulley 21 b of the PRI pulley 21 and aV-shaped sheave surface formed by the fixed pulley 22 a and the movablepulley 22 b of the SEC pulley 22.

The variator 20 constitutes a belt continuously variable transmissionmechanism for shifting by changing each of groove widths of the PRIpulley 21 and the SEC pulley 22 to change a winding diameter of the belt23.

In such a variator 20, the movable pulley 21 b operates to change thegroove width of the PRI pulley 21 by controlling the PRI pressure.Further, the movable pulley 22 b operates to change the groove width ofthe SEC pulley 22 by controlling the SEC pressure.

The PRI pressure and the SEC pressure are generated in a hydrauliccontrol circuit 11 using a line pressure PL as a source pressure. Theline pressure PL may be applied as one of the PRI pressure and the SECpressure. In this case, the variator 20 can be configured as a variatorof a single pressure adjusting type.

The sub-transmission mechanism 30 is a stepped transmission mechanismand has two forward and one reverse gear positions. The sub-transmissionmechanism 30 has a first speed and a second speed having a smaller speedratio than the first speed as the forward gear positions. Thesub-transmission mechanism 30 is provided in series on an output side ofthe variator 20 in a power transmission path from the engine 1 to thedrive wheels 5. The sub-transmission mechanism 30 may be directlyconnected to the variator 20 or may be indirectly connected to thevariator 20 via another configuration such as a gear train.

The sub-transmission mechanism 30 is provided with a planetary gearmechanism 31 and a plurality of friction engaging elements including alow brake 32, a high clutch 33 and a reverse brake 34. The gear positionof the sub-transmission mechanism 30 is changed by adjusting hydraulicpressures supplied to the plurality of friction engaging elements andchanging engaged/disengaged states of the plurality of friction engagingelements.

For example, if the low brake 32 is engaged and the high clutch 33 andthe reverse brake 34 are disengaged, the gear position is set to thefirst speed. Further, if the high clutch 33 is engaged and the low brake32 and the reverse brake 34 are disengaged, the gear position is set tothe second speed. Further, if the reverse brake 34 is engaged and thelow brake 32 and the high clutch 33 are disengaged, the gear position isset to a reverse speed.

In the vehicle, the speed ratio is changed in each of the variator 20and the sub-transmission mechanism 30. Thus, in the vehicle, a shift iscarried out according to a through speed ratio which is an overall speedratio of the variator 20 and the sub-transmission mechanism 30. Thethrough speed ratio is a speed ratio obtained by multiplying the speedratio of the variator 20 by the speed ratio of the sub-transmissionmechanism 30.

In the variator 20 and the sub-transmission mechanism 30, the variator20 has slower shift responsiveness than the sub-transmission mechanism30. Slow shift responsiveness means a large delay in responsiveness ofan actual speed ratio to a shift command.

Thus, even if a shift command is simultaneously output to the variator20 and the sub-transmission mechanism 30, the actual speed ratio changesat a later timing in the variator 20 than in the sub-transmissionmechanism 30. Further, even if a similar shift command is output to thevariator 20 and the sub-transmission mechanism 30, a changing rate ofthe actual speed ratio is lower in the variator 20 than in thesub-transmission mechanism 30.

The variator 20 constitutes an automatic transmission mechanism 3together with the sub-transmission mechanism 30. The variator 20 and thesub-transmission mechanism 30 may be configured as structurallyindividual transmission mechanisms.

The vehicle further includes an oil pump 10, the hydraulic controlcircuit 11 and a controller 12.

The oil pump 10 feeds oil under pressure. A mechanical oil pumpconfigured to be driven by the power of the engine 1 can be used as theoil pump 10.

The hydraulic control circuit 11 adjusts a pressure of the oil fed underpressure from the oil pump 10, i.e. a hydraulic pressure and transmitsthe adjusted hydraulic pressure to each component of the variator 20 andthe sub-transmission mechanism 30. In the hydraulic control circuit 11,for example, the line pressure LP, the PRI pressure and the SEC pressureare adjusted.

The controller 12 is an electronic control device and controls thehydraulic control circuit 11. Output signals of rotation sensors 41, 42and 43 are input to the controller 12.

The rotation sensor 41 is a variator input-side rotation sensor fordetecting a rotation speed on an input side of the variator 20. Therotation sensor 42 is a variator output-side rotation sensor fordetecting a rotation speed on an output side of the variator 20. Therotation sensor 42 specifically detects the rotation speed on the outputside of the variator 20 and on an input side of the sub-transmissionmechanism 30. The rotation sensor 43 is a sub-transmission mechanismoutput-side rotation sensor for detecting a rotation speed on an outputside of the sub-transmission mechanism 30.

The rotation speed on the input side of the variator 20 is specificallya rotation speed of an input shaft of the variator 20. The rotationspeed on the input side of the variator 20 may be a rotation speed at aposition, for example, at a side opposite to the variator 20 across agear train in the aforementioned power transmission path. The sameapplies also for the rotation speed on the output side of the variator20 and the rotation speed on the output side of the sub-transmissionmechanism 30.

Besides these, output signals of an accelerator pedal opening sensor 44,an inhibitor switch 45, an engine rotation sensor 46 and the like areinput to the controller 12.

The accelerator pedal opening sensor 44 detects an accelerator pedalopening APO representing an operated amount of an accelerator pedal. Theinhibitor switch 45 detects the position of a select lever. The enginerotation sensor 46 detects a rotation speed Ne of the engine 1. Thecontroller 12 can detect a vehicle speed VSP on the basis of the outputsignal of the rotation sensor 43.

The controller 12 generates a shift control signal on the basis of thesesignals and outputs the generated shift control signal to the hydrauliccontrol circuit 11. The hydraulic control circuit 11 controls the linepressure PL, the PRI pressure and the SEC pressure and switcheshydraulic pressure paths on the basis of the shift control signal fromthe controller 12.

In this way, the hydraulic pressure corresponding to the shift controlsignal is transmitted from the hydraulic control circuit 11 to eachcomponent of the variator 20 and the sub-transmission mechanism 30. As aresult, the speed ratios of the variator 20 and the sub-transmissionmechanism 30 are changed to speed ratios corresponding to the shiftcontrol signal, i.e. target speed ratios.

The transmission 100 is an automatic transmission and configured toinclude the hydraulic control circuit 11 and the controller 12 forcontrolling the speed ratios in this way, and the rotation sensors 41,42 and 43 besides the variator 20 and the sub-transmission mechanism 30.The transmission 100 may be configured to further include, for example,pressure sensors for detecting hydraulic pressures supplied to theplurality of friction engaging elements of the sub-transmissionmechanism 30 and the like.

FIG. 2 is a graph showing an example of a shift map. In FIG. 2, a totalload line which is a shift line when the accelerator pedal openingAPO=8/8, a partial line which is a shift line when the accelerator pedalopening APO=4/8 and a coast line which is a shift line when theaccelerator pedal opening APO=0 are illustrated as shift lines.

The transmission 100 is shifted on the basis of the shift map. In theshift map, an operating point of the transmission 100 is shown accordingto the vehicle speed VSP and a rotation speed Npri. The rotation speedNpri is a rotation speed of the PRI pulley 21.

The transmission 100 is shifted in accordance with the shift lineselected according to the accelerator pedal opening APO. Thus, the shiftline is set for each accelerator pedal opening APO in the shift map. Inthe shift map, the speed ratio of the transmission 100, i.e. the throughspeed ratio, is represented by a gradient of a line connecting theoperating point of the transmission 100 and a zero point of the shiftmap.

When the gear position of the sub-transmission mechanism 30 is the firstspeed, the transmission 100 can be shifted between a low-speed modelowest line obtained by maximizing the speed ratio of the variator 20and a low-speed mode highest line obtained by minimizing the speed ratioof the variator 20.

When the gear position of the sub-transmission mechanism 30 is thesecond speed, the transmission 100 can be shifted between a high-speedmode lowest line obtained by maximizing the speed ratio of the variator20 and a high-speed mode highest line obtained by minimizing the speedratio of the variator 20.

A mode switch shift line Lm used to shift the sub-transmission mechanism30 is further set in the shift map. In this example, the mode switchshift line Lm is set at the low-speed mode highest line. A region R1represents a region having a lower vehicle speed VSP than the modeswitch shift line Lm and a region R2 represents a region having a highervehicle speed VSP than the mode switch shift line Lm.

The controller 12 starts shifting the sub-transmission mechanism 30 whenthe operating point of the transmission 100 crosses the mode switchshift line Lm. Further, as the sub-transmission mechanism 30 is shifted,the controller 12 carries out a coordinated shift for changing the speedratio of the variator 20 in a direction opposite to a changing directionof the speed ratio of the sub-transmission mechanism 30 so that thethrough speed ratio reaches a target through speed ratio.

Specifically, the controller 12 starts a 1-2 shift for upshifting thegear position of the sub-transmission mechanism 30 from the first speedto the second speed when the operating point of the transmission 100crosses the mode switch shift line Lm from the region R1 toward theregion R2. Further, in this case, the controller 12 specifically carriesout a coordinated shift for changing the speed ratio of the variator 20in a direction to increase the speed ratio, i.e. toward a Low side. Thecoordinated shift may include a shift of the sub-transmission mechanism30.

A 2-1 shift for downshifting the gear position of the sub-transmissionmechanism 30 from the second speed to the first speed is, for example,carried out according to an accelerator pedal operation or a selectlever operation of a driver. In the case of carrying out the 2-1 shift,a shift for changing the speed ratio in a direction to decrease thespeed ratio, i.e. toward a High side can be carried out in the variator20. Such a shift may be carried out as a coordinated shift for changingthe speed ratio of the variator 20 such that the through speed ratioreaches the target through speed ratio.

Next, an example of a control executed by the controller 12 is describedusing a flow chart shown in FIG. 3. The controller 12 can repeatedlyperform a process shown in this flow chart at every infinitesimal timeinterval. A process after the start of the 1-2 shift is described inFIG. 3.

In Step S1, the controller 12 determines whether or not thesub-transmission mechanism 30 is in an inertia phase including the startof the inertia phase of the sub-transmission mechanism 30. The inertiaphase is a shift stage in which the speed ratio of the sub-transmissionmechanism 30 actually changes, and a coordinated shift is carried out inthe inertia phase.

Such determination can be made, for example, by determining whether ornot a target value of the hydraulic pressure supplied to the high clutch33, which is the friction engaging element to be engaged during a shift,is larger than a predetermined value. The predetermined value is a valuefor determining the re-engagement of the friction engaging elements inthe sub-transmission mechanism 30 and can be set in advance through anexperiment or the like. In the case of carrying out the 1-2 shift, theengaged friction engaging element is switched from the low brake 32 tothe high clutch 33 in the sub-transmission mechanism 30.

If the determination in Step S1 is negative, the controller 12temporarily ends the process of this flow chart. If the determination inStep S1 is affirmative, the process proceeds to Step S2.

In Step S2, the controller 12 sets a target sub-speed ratio, which is atarget speed ratio of the sub-transmission mechanism 30, on the basis ofa target through speed ratio and an actual speed ratio of the variator20.

The target through speed ratio is, for example, set such that thethrough speed ratio is constant even if the sub-transmission mechanism30 is shifted. Thus, a mode switch speed ratio, which is a speed ratiocorresponding to the mode switch shift line Lm, can be applied as thetarget through speed ratio. The actual speed ratio of the variator 20can be calculated on the basis of outputs of the rotation sensors 41 and42.

The processing of Step S2 is performed in carrying out a coordinatedshift by being performed in response to the start of the inertia phase,and is performed during the inertia phase, specifically only during theinertia phase.

In Step S3, the controller 12 calculates a target SEC rotation speed.The target SEC rotation speed is a target value of a SEC rotation speed,and the SEC rotation speed is a rotation speed of the SEC pulley 22. Thetarget SEC rotation speed is calculated by multiplying the targetsub-speed ratio by an output-side rotation speed of the sub-transmissionmechanism 30.

The target SEC rotation speed is calculated in Step S3 because thetarget SEC rotation speed can be treated as a parameter equivalent tothe target sub-speed ratio by assuming that the output-side rotationspeed of the sub-transmission mechanism 30 is constant during the 1-2shift.

In Step S4, the controller 12 determines whether or not a firstcorrection necessity determination is satisfied. In the first correctionnecessity determination, whether or not the target speed ratio and theactual speed ratio in the variator 20 at the start of the inertia phasediffer is determined, and the determination is satisfied if thesediffer.

If the determination in Step S4 is affirmative, the process proceeds toStep S5. In this case, the controller 12 corrects the target SECrotation speed. The correction of the target SEC rotation speed isdescribed later. After Step S5 or negative determination in Step S4, theprocess proceeds to Step S6.

In Step S6, the controller 12 determines whether or not a secondcorrection necessity determination is satisfied. In the secondcorrection necessity determination, whether or not the target throughspeed ratio and the through speed ratio deviate is determined, and thedetermination is satisfied if these deviate.

Whether or not the target through speed ratio and the through speedratio deviate is specifically determined by determining whether or not ashift speed of the sub-transmission mechanism 30 has reached a lowerlimit value. The lower limit value is described later.

If the determination in Step S6 is affirmative, the process proceeds toStep S7 and the controller 12 corrects a shift speed of the variator 20.The correction of the shift speed of the variator 20 is described later.After Step S7 or negative determination in Step S6, the process proceedsto Step S8.

In Step S8, the controller 12 determines whether or not a transition ofthe target SEC rotation speed has been ended. Here, since a second-speedspeed ratio is “1” in the sub-transmission mechanism 30, the target SECrotation speed transitions to the output-side rotation speed of thesub-transmission mechanism 30 in the 1-2 shift.

Thus, in Step S8, the controller 12 specifically determines whether ornot the target SEC rotation speed is equal to or lower than theoutput-side rotation speed of the sub-transmission mechanism 30. If thedetermination in Step S8 is negative, the process proceeds to Step S9.

In Step S9, the controller 12 determines whether or not the inertiaphase has been ended. In the 1-2 shift, the inertia phase is ended whenthe sub-speed ratio, which is the speed ratio of the sub-transmissionmechanism 30, reaches the second-speed speed ratio, thus when an actualSEC rotation speed has reached the output-side rotation speed of thesub-transmission mechanism 30.

Thus, in Step S9, the controller 12 specifically determines whether ornot the actual SEC rotation speed is equal to or lower than theoutput-side rotation speed of the sub-transmission mechanism 30. If thedetermination in Step S9 is negative, the sub-transmission mechanism 30is still in the inertia phase. Thus, the controller 12 temporarily endsthe process of this flow chart.

In the case of affirmative determination in Step S8 or Step S9, a statewhere the target sub-speed ratio may be fixed at the second-speed speedratio and the target SEC rotation speed may be fixed at the output-siderotation speed of the sub-transmission mechanism 30 can be judged.

Thus, in this case, the process proceeds to Step S10 and the controller12 sets the target sub-speed ratio to the second-speed speed ratio andsets the target SEC rotation speed to the output-side rotation speed ofthe sub-transmission mechanism 30. After Step S10, the controller 12temporarily ends the process of this flow chart.

Next, the target SEC rotation speed correction performed in Step S5described above is described using FIGS. 4A and 4B.

FIG. 4A is a first chart showing the target SEC rotation speedcorrection. FIG. 4B is a second chart showing the target SEC rotationspeed correction. FIG. 4A shows a case where the actual speed ratio islower than the target speed ratio in the variator 20 at the start of theinertia phase. FIG. 4B shows a case where the actual speed ratio ishigher than the target speed ratio in the variator 20 at the start ofthe inertia phase.

In the case of FIG. 4A, unless the correction is performed, the targetSEC rotation speed is calculated to be higher than a first-speedengagement SEC rotation speed since the actual speed ratio is lower thanthe target speed ratio in the variator 20 at the start of the inertiaphase. The first-speed engagement SEC rotation speed is a SEC rotationspeed obtained in the gear position engaged in the sub-transmissionmechanism 30 before the start of the inertia phase after the shift ofthe sub-transmission mechanism 30 is started. As a result, the targetSEC rotation speed suddenly changes at the start of the inertia phase.

In the case of FIG. 4B, unless the correction is performed, the targetSEC rotation speed is calculated to be lower than the first-speedengagement SEC rotation speed since the actual speed ratio is higherthan the target speed ratio in the variator at 20 the start of theinertia phase. As a result, also in this case, the target SEC rotationspeed suddenly changes at the start of the inertia phase.

Thus, the controller 12 performs a correction to transition from thefirst-speed engagement SEC rotation speed at the start of the inertiaphase to an initial target SEC rotation speed by changing the target SECrotation speed by a predetermined change amount when the target speedratio and the actual speed ratio differ in the variator 20 at the startof the inertia phase.

The initial target SEC rotation speed is a target SEC rotation speedwhen such a correction is not performed; hence the target SEC rotationspeed calculated by the controller 12 in Step S3 described above.

Such a correction can be performed, for example, by setting the targetSEC rotation speed to the first-speed engagement SEC rotation speed atthe start of the inertia phase and gradually reducing the target SECrotation speed by the predetermined change amount according to adifference between the initial target SEC rotation speed and thefirst-speed engagement rotation speed until the target SEC rotationspeed reaches the initial target SEC rotation speed.

In the case of FIG. 4A, the predetermined change amount can be set toincrease as a difference obtained by subtracting the first-speedengagement SEC rotation speed from the initial target speed ratiodecreases, including a case where a sign becomes negative.

In the case of FIG. 4B, the predetermined change amount can be set toincrease as a difference obtained by subtracting the initial target SECrotation speed from the first-speed engagement SEC rotation speedincreases.

A case where the target speed ratio and the actual speed ratio differ inthe variator 20 at the start of the inertia phase may be a case wherethe magnitude of a difference between the first-speed engagementrotation speed and the initial target SEC rotation speed is larger thana predetermined value at the start of the inertia phase. Thepredetermined value is a value for considering an error, individualdifferences, a margin and the like and can be set in advance through anexperiment or the like.

As described above, the target SEC rotation speed can be treated as aparameter equivalent to the target sub-speed ratio. Thus, the controller12 performs a correction to transition from the first-speed speed ratioto an initial target sub-speed ratio by changing the target sub-speedratio by a predetermined change amount when the target speed ratio andthe actual speed ratio differ in the variator 20 at the start of theinertia phase.

Here, the first-speed speed ratio is a speed ratio obtained in the gearposition engaged in the sub-transmission mechanism 30 before the startof the inertia phase after the shift of the sub-transmission mechanism30 is started. Further, the initial target sub-speed ratio is a targetsub-speed ratio when such a correction is not performed; hence thetarget sub-speed ratio set by the controller 12 in Step S2 describedabove.

Next, the correction of the shift speed of the variator 20 performed inStep S7 described above is described using FIG. 5.

At timing T1, the shift speed of the sub-transmission mechanism 30reaches the lower limit value and the second correction necessitydetermination is satisfied. The shift speed of the sub-transmissionmechanism 30 is, in other words, the magnitude of a target SEC rotationspeed change rate, i.e. the magnitude of a gradient of the target SECrotation speed.

The lower limit value is specifically set as a minimum value of theshift speed at which judder does not occur in shifting thesub-transmission mechanism 30. The judder is a phenomenon in which aforce does not smoothly act on a friction surface to cause abnormalnoise or vibration in a friction clutch or friction brake fortransmitting power by friction.

The lower limit value is set as described above for the followingreason. Specifically, in the coordinated shift, if the shift speed ofthe variator 20 is low, the shift speed of the sub-transmissionmechanism 30 is also restricted to be low. Further, in thesub-transmission mechanism 30, judder possibly occurs in the frictionengaging elements if the shift speed decreases.

On the other hand, if the shift speed of the sub-transmission mechanism30 reaches the lower limit value, it is no longer possible to furtherreduce the shift speed of the sub-transmission mechanism 30 by thecoordinated shift. Thus, there is a possibility of losing thecoordinated shift. As a result, the target through speed ratio and thethrough speed ratio possibly deviate.

Thus, the controller 12 corrects the shift speed of the variator 20 attiming T1. This correction is a correction to increase the shift speedof the variator 20 higher than the shift speed at timing T1 at which thedeviation between the through speed ratio and the target through speedratio is detected or predicted. In other words, this correction is acorrection to make the magnitude of a gradient of the actual speed ratioof the variator 20 larger than that of the gradient at timing T1 asshown in FIG. 5.

Such a correction can be specifically performed, for example, bychanging a feedback correction amount to increase the shift speed of thevariator 20 in a feedback control of controlling the actual speed ratioof the variator 20 to the target speed ratio.

The target sub-speed ratio is calculated on the basis of the actualspeed ratio of the variator 20 in Step S2 described above. Thus, byperforming the correction to increase the shift speed of the variator20, a correction to increase the shift speed of the target sub-speedratio is also performed via this correction. In other words, as shown inFIG. 5, a correction is also performed to make the magnitude of thegradient of the target SEC rotation speed larger than that of thegradient at timing T1. Since the shift speed of the sub-transmissionmechanism 30 can be prevented from being fixed at the lower limit valuein this way, it is possible to prevent the coordinated shift from beinglost.

Next, main functions and effects of the transmission 100 are described.The transmission 100 includes the sub-transmission mechanism 30 servingas a first transmission mechanism, the variator 20 serving as a secondtransmission mechanism having lower shift responsiveness than the firsttransmission mechanism, and the controller 12 serving as a shift controlunit configured to carry out a coordinated shift such that the throughspeed ratio reaches the target through speed ratio. The controller 12serving as the shift control unit sets the target sub-speed ratio on thebasis of the target through speed ratio and the actual speed ratio ofthe variator 20 in carrying out the coordinated shift.

According to the transmission 100 thus configured, since the targetspeed ratio of the sub-transmission mechanism 30 having higher shiftresponsiveness than the variator 20, i.e. the target sub-speed ratio, isset on the basis of the target through speed ratio and the actual speedratio of the variator 20, the target through speed ratio and the actualthrough speed ratio can be prevented from deviating. Thus, even if thesub-transmission mechanism 30 serving as the first transmissionmechanism and the variator serving as the second transmission mechanismdiffer in shift responsiveness, a loss of the coordinated shift can besuppressed. As a result, a sense of incongruity given to a driver can beeliminated.

When the variator 20 is upshifted or downshifted according to theaccelerator pedal operation, the actual speed ratio follows the targetspeed ratio with a delay in the variator 20. Thus, the actual speedratio and the target speed ratio do not match.

If the target sub-speed ratio is set on the basis of the target throughspeed ratio and the actual speed ratio of the variator 20 before theshift of the sub-transmission mechanism 30 is started and the inertiaphase is started in this state, it is instructed to suddenly change thetarget sub-speed ratio before the start of the inertia phase. As aresult, the friction engaging elements of the sub-transmission mechanism30 are unnecessarily set in a slip state or a torque of the engine 1varies.

In view of such a situation, in the transmission 100, the controller 12serving as the shift control unit sets the target sub-speed ratio on thebasis of the target through speed ratio and the actual speed ratio ofthe variator 20 during the inertia phase in the sub-transmissionmechanism 30 in carrying out the coordinated shift. In the transmission100, the sub-transmission mechanism 30 serving as the first transmissionmechanism is a stepped transmission mechanism for changing the speedratio by re-engaging the friction engaging elements, and the variator 20serving as the second transmission mechanism is a continuously variabletransmission mechanism including the PRI pulley 21, the SEC pulley 22and the belt 23 wound on the PRI pulley 21 and the SEC pulley 22.

According to the transmission 100 thus configured, it is possible toprevent the deterioration of drivability caused by unnecessarily settingthe friction engaging elements of the sub-transmission mechanism 30 inthe slip state before the start of the inertia phase or due to avariation of the torque of the engine 1.

In the transmission 100, the controller 12 serving as the shift controlunit further performs a correction to transition from the speed ratioobtained in the gear position engaged in the sub-transmission mechanism30 before the start of the inertia phase to the initial target sub-speedratio, i.e. the target sub-speed ratio set by the controller 12 servingas the shift control unit by changing the target sub-speed ratio by thepredetermined change amount after the shift of the sub-transmissionmechanism 30 is started when the target speed ratio and the actual speedratio differ in the variator 20 at the start of the inertia phase.

According to the transmission 100 thus configured, a situation can beprevented in which it is instructed to suddenly change the targetsub-speed ratio at the start of the inertia phase and, as a result,drivability is deteriorated. Further, since the target sub-speed ratiocan be gradually changed, a situation can be prevented in which thecoordinated shift is lost and a sense of incongruity is given to thedriver due to a sudden change of the target sub-speed ratio.

In the transmission 100, the sub-transmission mechanism 30 serving asthe first transmission mechanism is a stepped transmission mechanism forchanging the speed ratio by re-engaging the friction engaging elements,and the variator 20 serving as the second transmission mechanism is acontinuously variable transmission mechanism including the PRI pulley21, the SEC pulley 22 and the belt 23 wound on the PRI pulley 21 and theSEC pulley 22. Further, in the transmission 100, the controller 12serving as the shift control unit further sets the lower limit value forthe shift speed of the sub-transmission mechanism 30 in carrying out thecoordinated shift.

According to the transmission 100 thus configured, a reduction of theshift speed of the sub-transmission mechanism 30 and the occurrence ofjudder in the friction engaging elements of the sub-transmissionmechanism 30 can be prevented or suppressed in carrying out thecoordinated shift.

In the transmission 100, the lower limit value is set as a minimum valueof the shift speed at which judder does not occur in shifting thesub-transmission mechanism 30.

According to the transmission 100 thus configured, the occurrence ofjudder in the sub-transmission mechanism 30 can be prevented in carryingout the coordinated shift. Further, since the lower limit value is setas low as possible, it can be made more difficult for the shift speed ofthe sub-transmission mechanism 30 to reach the lower limit value. Thus,the shift speed of the sub-transmission mechanism 30 cannot furtherdecrease after reaching the lower limit value, with the result that itis also possible to suppress the occurrence of a situation in which thetarget through speed ratio and the through speed ratio deviate.

In the transmission 100, the controller 12 serving as the shift controlunit increases the shift speed of the variator 20 higher than the shiftspeed at the time of detecting or predicting the deviation between thetarget through speed ratio and the through speed ratio if the deviationbetween the target through speed ratio and the through speed ratio isdetected or predicted. The deviation between the target through speedratio and the through speed ratio is detected or predicted when theshift speed of the sub-transmission mechanism 30 reaches the lower limitvalue.

According to the transmission 100 thus configured, since the shift speedof the sub-transmission mechanism 30 can be prevented from being fixedat the lower limit value as described above using FIG. 5, a loss of thecoordinated shift can be prevented.

In the transmission 100, the controller 12 serving as the shift controlunit may be configured, when judder occurs in shifting thesub-transmission mechanism 30 at a shift speed higher than the lowerlimit value, to set the lower limit value to a shift speed higher thanthe shift speed at which this judder occurs. A known technique oranother appropriate technique may be applied to determine the occurrenceof judder.

In this way, if judder occurs at the shift speed higher than theinitially set lower limit value in the sub-transmission mechanism 30 dueto a variation or aging caused by individual differences of thetransmission 100, the lower limit value can be updated. Specifically,the lower limit value can be a variable value which is updated byso-called learning without being a fixed value.

Thus, according to the transmission 100 thus configured, it is possibleto prevent the occurrence of judder while preventing the shift speed ofthe sub-transmission mechanism 30 from easily reaching the lower limitvalue to lose the coordinated shift as a result of setting the lowerlimit value higher than necessary.

Although the embodiment of the present invention has been describedabove, the above embodiment is merely an illustration of one applicationexample of the present invention and not intended to limit the technicalscope of the present invention to the specific configuration of theabove embodiment.

Although the sub-transmission mechanism 30 has been described to havetwo forward gear positions in the above embodiment, the sub-transmissionmechanism 30 may, for example, have three or more forward gearpositions.

Although the controller 12 is configured as the shift control unit inthe above embodiment, the shift control unit may be, for example,composed of a plurality of controllers.

The predetermined change amount only has to be set so that the targetsub-speed ratio does not suddenly change. Thus, it is, for example, alsopossible to set the predetermined change amount at a fixed value.

Although the drive source is the engine 1 in the above embodiment, thedrive source may be, for example, a motor or a combination of an engineand a motor.

The present application claims a priority based on Japanese PatentApplication No. 2015-125534 filed with the Japan Patent Office on Jun.23, 2015, all the contents of which are hereby incorporated byreference.

1.-8. (canceled)
 9. A transmission, comprising: a stepped transmissionmechanism provided in a power transmission path for transmitting powerfrom a drive source of a vehicle to drive wheels, the steppedtransmission mechanism changing a speed ratio by re-engaging frictionengaging elements; a continuously variable transmission mechanismincluding two pulleys and a belt wound on the two pulleys, thecontinuously variable transmission mechanism being provided in serieswith the stepped transmission mechanism in the power transmission path,the continuously variable transmission mechanism having lower shiftresponsiveness than the stepped transmission mechanism; and a controllerconfigured to carry out a coordinated shift for changing a speed ratioof the continuously variable transmission mechanism in a directionopposite to a changing direction of the speed ratio of the steppedtransmission mechanism as the stepped transmission mechanism is shiftedso that a through speed ratio, the through speed ratio being an overallspeed ratio of the stepped transmission mechanism and the continuouslyvariable transmission mechanism, reaches a target through speed ratio;the controller setting a target speed ratio of the stepped transmissionmechanism on the basis of the target through speed ratio and an actualspeed ratio of the continuously variable transmission mechanism duringan inertia phase in the stepped transmission mechanism in carrying outthe coordinated shift, and the controller further performing acorrection to transition from a speed ratio before a start of theinertia phase to the target speed ratio set by the controller during theinertia phase by gradually changing the target speed ratio of thestepped transmission mechanism by a predetermined change amount so as toprevent the target speed ratio of the stepped transmission mechanismfrom suddenly changing when a target speed ratio and the actual speedratio differ in the continuously variable transmission mechanism at thestart of the inertia phase.
 10. The transmission according to claim 9,wherein: the controller further sets a lower limit value for a shiftspeed of the stepped transmission mechanism in carrying out thecoordinated shift.
 11. The transmission according to claim 10, wherein:the lower limit value is set as a minimum value of the shift speed, atwhich judder does not occur, in shifting the stepped transmissionmechanism.
 12. The transmission according to claim 11, wherein: thecontroller sets a shift speed of the continuously variable transmissionmechanism higher than a shift speed at the time of detecting orpredicting a deviation between the target through speed ratio and thethrough speed ratio when the deviation between the target through speedratio and the through speed ratio is detected or predicted.
 13. Thetransmission according to claim 10, wherein: the controller sets thelower limit value to a shift speed higher than a shift speed, at whichjudder occurs, if the judder occurs in shifting the stepped transmissionmechanism at a shift speed higher than the lower limit value.
 14. Acontrol method for a transmission with a stepped transmission mechanismprovided in a power transmission path for transmitting power from adrive source of a vehicle to drive wheels, the stepped transmissionmechanism changing a speed ratio by re-engaging friction engagingelements, and a continuously variable transmission mechanism includingtwo pulleys and a belt wound on the two pulleys, the continuouslyvariable transmission mechanism being provided in series with thestepped transmission mechanism in the power transmission path, thecontinuously variable transmission mechanism having lower shiftresponsiveness than the stepped transmission mechanism, comprising:carrying out a coordinated shift for changing a speed ratio of thecontinuously variable transmission mechanism in a direction opposite toa changing direction of the speed ratio of the stepped transmissionmechanism as the stepped transmission mechanism is shifted so that athrough speed ratio, the through speed ratio being an overall speedratio of the stepped transmission mechanism and the continuouslyvariable transmission mechanism, reaches a target through speed ratio;setting a target speed ratio of the stepped transmission mechanism onthe basis of the target through speed ratio and an actual speed ratio ofthe continuously variable transmission mechanism during an inertia phasein the stepped transmission mechanism in carrying out the coordinatedshift; and performing a correction to transition from a speed ratiobefore a start of the inertia phase to the target speed ratio set duringthe inertia phase by gradually changing the target speed ratio of thestepped transmission mechanism by a predetermined change amount so as toprevent the target speed ratio of the stepped transmission mechanismfrom suddenly changing when a target speed ratio and the actual speedratio differ in the continuously variable transmission mechanism at thestart of the inertia phase.
 15. A transmission, comprising: a steppedtransmission mechanism provided in a power transmission path fortransmitting power from a drive source of a vehicle to drive wheels, thestepped transmission mechanism changing a speed ratio by re-engagingfriction engaging elements; a continuously variable transmissionmechanism including two pulleys and a belt wound on the two pulleys, thecontinuously variable transmission mechanism being provided in serieswith the stepped transmission mechanism in the power transmission path,the continuously variable transmission mechanism having lower shiftresponsiveness than the stepped transmission mechanism; and shiftcontrol means for carrying out a coordinated shift for changing a speedratio of the continuously variable transmission mechanism in a directionopposite to a changing direction of the speed ratio of the steppedtransmission mechanism as the stepped transmission mechanism is shiftedso that a through speed ratio, the through speed ratio being an overallspeed ratio of the stepped transmission mechanism and the continuouslyvariable transmission mechanism, reaches a target through speed ratio;the shift control means setting a target speed ratio of the steppedtransmission mechanism on the basis of the target through speed ratioand an actual speed ratio of the continuously variable transmissionmechanism during an inertia phase in the stepped transmission mechanismin carrying out the coordinated shift, and the shift control meansfurther performing a correction to transition from a speed ratio beforea start of the inertia phase to the target speed ratio set by the shiftcontrol means during the inertia phase by gradually changing the targetspeed ratio of the stepped transmission mechanism by a predeterminedchange amount so as to prevent the target speed ratio of the steppedtransmission mechanism from suddenly changing when a target speed ratioand the actual speed ratio differ in the continuously variabletransmission mechanism at the start of the inertia phase.